Over the years, tobacco growers have utilized various agricultural practices to improve the quality and yield of their crop. Removal of the tobacoo tops has been historically practiced as one method of increasing the yield of tobacco leaves. Upon removal of the plant tops, the energy and growth normally translocated to the plant tops for inflorescence is diverted into the leaves, resulting in greater numbers and size of the leaves, thus increasing the economic yield. The nature of any plant is to reproduce itself; therefore, when the tobacco infloresence is removed, a physiological process known as `apical dominance` is triggered. This phenomena results in accelerated growth of the uppermost axillary buds (suckers) which exists at each leaf axil. If allowed to develop unhindered, these suckers would each develop infloresence and in turn result in leaf yield reductions. In earlier years this sucker growth was removed by hand.
In recent years, tobacco growers in the U.S.A. have relied on chemicals to control and minimize sucker growth.
The major portion of flue-cured and burley tobacco (.about.820,000 acres) is chemically treated annually for the control of suckers.
One chemical method of sucker (axillary bud) control consists in the topical contact application of fatty alcohols (nominal C.sub.8 -C.sub.10), mineral oils and similar inhibiting agents directly to the axillary buds before and during their initial development stages. These topical agents have some phytotoxic action on the leaves and thus should be carefully applied preferably to the buds. Leaf contact should be avoided. Generally these agents are applied to the initial "topping" areas and by dripping down the stem these agents contact the axillary buds adjacent to the main stem. However, any contact with the leaves by the dripping agents may cause chlorosis and other phytotoxic effects as well as other degradation of leaf quality. Further, as these contact agents drip and accumulate at the base, they often have caused necrosis of the entire stem base and kill the plant. A further drawback to the present topical chemical budinhibition method is that some of these aspects require the skillful manual application of the agent at the required location and require considerable fairly skilled hand labor which is economically unsuitable in large scale tobacco culture.
Another method for sucker control in tobacco cultivation has been by the systemic application, after topping, of maleic hydrazide (1,2-Dihydro-3,6-pyridazindione). The maleic hydrazide (MH) is applied, in the form of its salts or amine complexes, by spraying onto the plants after the manual topping of the initial inflorescence. The maleic hydrazide (MH) is systemically absorbed through the leaves and has been effective for inhibiting the development of the axillary buds.
However, as noted in the Merck Index 8th Edition, Page 640, this material, as are most hydrazides, is toxic. It has produced CNS disturbances under acute exposure conditions and liver damage on chronic exposure, in experimental animals. Thus use of this agent under field conditions, should be properly supervised. Use of the material despite its economic importance is under review and in some countries is prohibited.